In hydrocarbon industry applications, such as offshore pipeline pre-commissioning procedures and well fracturing operations, servicing fluids including seawater and fresh water may be left untreated or may be rendered biologically inert by treating the fluids using chemical biocides.
In offshore pipeline applications, a water-based servicing fluid may be used to flood the pipeline during installation or to flood and hydrostatically test the pipeline once installed. During installation, the pipeline is laid on the seabed and then flooded with seawater, or in the case of alloy pipelines, fresh water. Once a pipeline is flooded, subsea connections can then be made. In particular, divers or remotely operated vehicles (ROVs) physically open the pipeline and connect it to a wellhead, subsea template, or riser system, for example. When making subsea connections to an alloy pipeline, it is undesirable for the seawater to contact the inner pipeline surfaces because seawater may corrode the pipeline. Therefore, the alloy pipeline is flooded with fresh water that includes a slug of gelled water at each end. As such, when the end of the pipeline is opened up for subsea connections to be made, the gel barrier prevents seawater from ingressing into the pipeline and mixing with the fresh water. After all subsea connections are made, additional water is pumped into the pipeline to hydrostatically test the structural integrity of the pipeline and any connected components. Once installation and testing are complete, the water contained within the pipeline is displaced and, in some cases, disposed of to sea.
At any point where water is being introduced into the pipeline, whether in the flooding stage or in the hydrostatic test stage, this water is typically filtered and treated with a chemical biocide to disinfect the water. The purpose of such treatment is to prevent bacteria and biological growth from causing damage to the pipeline internal surface. However, due to environmental laws and regulations, seawater used for hydrostatic testing in a number of locations, such as the Gulf of Mexico, cannot be disposed of to sea if it contains any chemical biocides. Therefore, untreated seawater is used, which permits organic growth in the pipeline, which may constrict and/or corrode the pipeline. This can have a detrimental effect on the available flow rates of the pipeline once in service. Although discharge of water containing chemical biocides is still permitted in other parts of the world, many countries are beginning to follow the lead of the Gulf of Mexico by prohibiting the discharge of chemical biocide treated water to sea because such discharge may harm marine life. Therefore, a need exists for a fluid treatment method that complies with environmental requirements and is not harmful to marine life if discharged to the ocean.
Chemical biocides are also used during pre-commissioning procedures for pipelines installed onshore. Disposal of water containing chemical biocides on land is also prohibited in some environmentally sensitive regions of the United States. In regions where no prohibitions exist, disposing of water containing chemical biocides is still undesirable in that it may harm wildlife and contaminate underground water. Therefore, a need exists for an alternative, environmentally friendly method of disinfecting fluid.
Fluids treated with chemical biocides are also used in well bore servicing operations, such as fracturing a formation, for example. These operations are often conducted in remote locations where water is scarce and must be transported to the well site, which is costly. Typically, the water is filtered and treated with chemical biocides to prevent bacterial growth during transportation and/or storage. In a fracturing application, a gelling agent and other constituents are added to the water prior to injection into the well bore. However, gel may act as a food source for any bacteria present in the fluid. Thus, if bacteria is present in the base water, the bacteria will eventually destroy the gel and negatively impact the fracturing operation. Hence, the water is generally disinfected with chemical biocides before its use in the fracturing operation.
Once the fracturing operation is complete, flowback fluid recovered from the well bore may be stored in man-made tanks or lined pits, but it is not disposed of to land due to the chemical biocides. This flowback fluid containing chemical biocides is typically not remediated for re-use or disposal because such remediation of the fluid using chemical treatments, for example, is cost prohibitive. Instead, the flowback fluid is generally removed from the well site for proper treatment and disposal. Specifically, proper disposal of fluids containing biocides requires removal of the biocide before the fluid can be returned to the environment.
Due to the scarcity of water in many remote locations, and the cost associated with transporting water to and from these well sites, it would be beneficial if formation fluid produced from the well could be used, or flowback fluid could be reused following a service operation. However, treatment of formation fluid and flowback fluid to remove bacteria is necessary for the success of many operations, such as fracturing. Hence, a need exists for a cost effective method of disinfecting produced fluid and flowback fluid for reuse in a well bore servicing operation, or for disposal to the environment.